High voltage electrical modules generate a lot of heat on printed circuit board (PCB) traces and high voltage components. This heat has to dissipate to a cold or base plate. Dissipating the heat requires a low thermal resistance between the PCB/high voltage component and the cold plate. Thermal resistance is inversely proportional to contact surface area.
In one existing approach to dissipating the generated heat, thermal pads are placed between the printed circuit board (PCB)/high voltage components and the cold plate. The thermal pads provide a path for heat to be removed while providing electrical isolation. Thermal pads require a certain compression to be effective. The compression to the thermal pad is created by the fasteners mounting the printed circuit board (PCB), and causes stress and deflection in the printed circuit board (PCB). Due to such deflection, the printed circuit board (PCB) can lose contact with the thermal pads, and thus have higher than expected thermal resistance to the cold plate.
A prior art mounting arrangement for mounting the printed circuit board (PCB)/high voltage component is shown in FIG. 1. A base or cold plate is shown at 10. A printed circuit board (PCB) 12 includes traces and high voltage components. Heat generated on the traces and high voltage components needs to be transferred to the base plate 10. The printed circuit board (PCB) includes wound components including ferrite cores 14, 16. Thin thermal pads 20 are placed between the printed circuit board (PCB) 12 and the base plate 10. A thick thermal pad 22 is placed between the ferrite core 16 and the base plate 10. Base plate 10 is shaped to receive PCB 12, and includes a recessed portion/depression 26 for receiving ferrite core 16. Thick thermal pad 22 is located at the bottom surface 28 of the depression 26 of base plate 10.
Thermal pads 20 and 22 are intended to close air gaps, while providing electrical isolation, when PCB 12 is secured by fasteners 24 to base plate 10. The compression to the thermal pads 20, 22 created by fasteners 24 mounting the printed circuit board (PCB) 12 causes stress and deflection in the printed circuit board (PCB) 12. Due to such deflection, the printed circuit board (PCB) 12 can lose contact with the thermal pads 20, and thus have higher than expected thermal resistance to the cold plate 10. This is shown at air gaps 30 between thin thermal pads 20 and PCB 12, which have very poor thermal transfer.
In another existing approach, additional fasteners may be used to try and reduce stress and deflection in the printed circuit board (PCB). However, additional bolts increase the size, weight, and cost of the assembly.
For the foregoing reasons, there is a need for an improved system and method for reducing thermal resistance between a power electronics printed circuit board and a base plate.
Background information may be found in U.S. Pat. Nos. 5,355,280; 5,679,457; 6,555,756; 7,206,205; and 7,365,273. Further background information may be found in U.S. Pub. Nos. 2003/0161105 and 2007/0004090, and in EP 1 739 741. Further background information may be found in “Gap Filler 1500 (Two-Part), Thermally Conductive Liquid Gap Filling Material,” The Berquist Company, 2008.